Electrochemical discharge machining device and machining method

ABSTRACT

An electrochemical discharge machining method may include electrolytically machining a tool fed by a three-dimensional tool feeder which can accurately feed a tool in three dimensions. The electrolytic machining may be performed in a current controlled mode, during which a concentration and a height of an electrolyte may be regulated. Further, the method may include performing electrochemical discharge machining of the workpiece using the machined tool in a voltage controlled mode.

FIELD OF THE INVENTION

The present invention relates to mechanical machining techniques, andmore particularly, to an electrochemical discharge machining devicecapable of performing a discharge machining as well as an electrolyticmachining in the same device, and a machining method. More specifically,the present invention relates to an electrochemical discharge machiningdevice and a machining method for performing an electrolytic machiningof a tool fed by a three-dimensional tool feeder which can accuratelyfeed a tool in three dimensions in a current controlled mode, regulate aconcentration and a height of an electrolyte, and perform anelectrochemical discharge machining of a workpiece using the machinedtool in a voltage controlled mode.

BACKGROUND OF THE INVENTION

Traditional mechanical machining techniques for machining workpieceshave included physical processes involving a lathe or milling. However,to perform machining of precision parts or easily breakable materials ofhigh hardness, various machining devices and methods have been devised.Machining techniques which can perform machining using electrical andchemical principles include electrolytic machining and a dischargemachining.

As for electrolytic machining, when a current is applied to theworkpiece (which serves as an anode) immersed in an alkaline electrolyteand a tool (which serves as a cathode), the workpiece can be machinedthrough the generated electrical and chemical reactions. Electrolyticpolishing and electrolytic grinding are examples of such processes.

The workpiece is slowly dissolved in the electrolyte through anoxidation reaction. As such, by adjusting an applied current density,the extent and rate of dissolving may be controlled. Such electrolyticmachining can be easily performed for metal materials with low carboncontents. Thus, heat resistant steel, cemented carbide, and high-tensilesteel, which are difficult to machine by physical processes because oftheir higher strength and lower carbon contents as compared with an ironmetal material, can be machined.

On the other hand, high hardness non-metallic materials have beenconventionally machined using diamond powder. Yet, this method requiresa long time period for machining, as well as the use of expensivediamond powder.

Alternatively, to machine such materials a discharge machining processhas been developed. In discharge machining a negative voltage is appliedto the workpiece and a positive voltage is applied to the tool. Then,when two materials are brought together at distance of a few of μm,sparking (i.e., dielectric breakdown) occurs. This event is referred toas discharge, which is used for machining the workpiece.

Conventional electrolytic machining and discharge machining are specialmachining techniques which use different methods and different devices.However, research to provide electrolytic machining and dischargemachining in the same device has been carried out in recent years, whichis commonly referred to as an electrochemical discharge machining.

A typical workpiece subjected to conventional electrochemical dischargemachining would include a non-metallic material having high hardness,which is subjected to discharge machining as described above. Thenon-metallic high hardness materials are utilized in fields requiringhigh accuracy, such as aerospace, precious metal processing, andautomobiles. In the conventional electrochemical discharge machiningdevice, the tool is machined in a separate machining device, and thenused for machining the non-metallic materials with high hardness.

In spite of developments improving the accuracy of machining, theworkpiece often cannot be accurately machined due to frequent desorptionof the tool. Further, such conventional electrochemical dischargemachining processes developed for the unified process of electrolyticmachining and discharge machining is disadvantageous in that theprocesses are complicated, and the tool is machined by a separatedevice.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to alleviate theabove noted problems and to provide an electrochemical dischargemachining device that is capable of simultaneously performing anelectrolytic machining and a discharge machining, thereby decreasingmachining errors.

According to one aspect of the present invention an electrochemicaldischarge machining device may include a three-dimensional tool feederor means, a position controller for electrically controlling movementsof the three-dimensional tool feeder, and a tool fixed at a lowerportion of the three-dimensional tool feeder. The device may alsoinclude an electrode having an opposite polarity to the tool, a powercontroller electrically connected to the position controller forapplying a current to the tool and the electrode, and an electrolyte forpromoting a certain electrochemical reaction between the tool and theelectrode immersed therein. Furthermore, an electrolytic bath includingthe electrolyte in which a workpiece is processed may be included andmay also include a jig by which the workpiece is upwardly positionedapart from a bottom of the bath.

More particularly, the electrolyte may be an aqueous alkaline solutionselected from the group consisting of potassium hydroxide, magnesiumhydroxide, sodium hydroxide, and calcium hydroxide. The tool may be madeof a metal material including at least one of tungsten and copper.Additionally, the electrode may include at least one of platinum, silverand gold. Also, the workpiece may include at least one of glass,ceramic, quartz, diamond, ruby, and sapphire.

In addition, the electrolytic bath may include an exhaust valve forremoving the electrolyte outside thereof, which may be at the bottom ofone side of the bath, for example. The electrochemical dischargemachining device may further include an electrolyte-supplying tank forsupplying the electrolyte to the electrolytic bath. Moreover, theelectrolyte-supplying tank may include a supply valve for regulating theflow of electrolyte to the electrolytic bath, which may be at a bottomside of the tank, for example.

A method aspect of the invention is for an electrochemical dischargemachining method and may include supplying an electrolyte to anelectrolytic bath at a predetermined height, immersing a tool at alength to be machined into the electrolyte, and electrolyticallymachining the tool by applying an electric field in a current controlledmode such that the tool and the electrode serve as an anode and acathode, respectively. Furthermore, a concentration and a height of theelectrolyte may be regulated based upon the material used for theworkpiece, and an electric field may be applied in a voltage controlledmode so that the tool and the electrode serve as a cathode and an anode,respectively. Additionally, the tool may be fed to the workpiece toperform an electrochemical discharge machining.

Further, the electrolyte may be an aqueous alkaline solution selectedfrom the group consisting of potassium hydroxide, magnesium hydroxide,sodium hydroxide, and calcium hydroxide. Also, the workpiece may includeat least one of glass, ceramic, quartz, diamond, ruby, and sapphire. Thetool may be made of a metal including at least one of tungsten andcopper. Also, the electrode may be made of a material including at leastone of platinum, silver and gold.

Further, the electrolytic bath may include an exhaust valve for removingthe electrolyte to the outside thereof, for example, at the bottom ofone side of the bath. Additionally, an electrolyte-supplying tank may beused for supplying the electrolyte to the electrolytic bath. Theelectroyte-supplying tank may be spaced apart from the bottom of thebath at a predetermined height and positioned over one side of the bath.Also, the electrolyte-supplying tank may include a supply valve forsupplying the electrolyte to the electrolytic bath, e.g., at a bottomside of the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic block diagram showing an electrochemical dischargemachining device according to the present invention;

FIG. 2 is a schematic diagram showing an electrolytic machining processaccording to the present invention;

FIG. 3 is a schematic diagram showing an electrochemical dischargemachining process according to the present invention; and

FIG. 4 is a flow chart of an electrochemical discharge machining processaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An electrochemical discharge machining device of the present inventionis shown in the schematic block diagram of FIG. 1, and a machiningmethod of the present invention is shown in the flow chart of FIG. 4. Asseen in FIGS. 1 and 4, the electrochemical discharge machining device200 includes a tool 10, an electrode 80 having an opposite polarity tothe tool 10, a three-dimensional tool feeder or means 20 for feeding thetool 10 fixed at a lower portion of the means, a position controller 30electrically connected to the three-dimensional tool feed means 20 forcontrolling movements of the means, and a power controller 40electrically connected to the position controller 30 for supplying adirect current to the tool 10 and the electrode 80.

The machining device 200 further includes an electrolytic bath 70 forcontaining an electrolyte 60. The direct current applied tool 10 and theelectrode 80 are immersed in the electrolyte 60 to cause a chemicalreaction through which the tool 10 is electrochemically machined.Meanwhile, a workpiece 50, which is upwardly positioned apart from abottom of the electrolytic bath 70 by a jig 71 and thus placed at thelower region of the bath, is subjected to electrochemical dischargemachining by the tool 10.

At one bottom side of the electrolytic bath 70 an exhaust valve 72 isprovided for removing the electrolyte 60 from the bath, and anelectrolyte-supplying tank 90 is spaced apart from the bottom of thebath at a predetermined height and positioned over one side of the bath.The electrolyte-supplying tank 90 is provided for supplying theelectrolyte 60 to the electrolytic bath 70. This may be done bycontrolling a supply valve 91 mounted on one side of the bottom of thetank, for example.

Further, the three-dimensional tool feed means 20 having the tool 10fixed at its lower portion is responsible for immersing the tool 10 intothe electrolyte 60 in the electrolytic bath 70, or for feeding the toolto a machining region of the workpiece 50. As such, the feed range ofthe tool is controlled through the electrically connected positioncontroller 30.

The power controller 40 is electrically connected to the positioncontroller 30 and controls the power supply used for machining. Thepower controller 40 also applies the direct current (or voltage) to thetool 10 and the electrode 80 to cause an electrolysis and anelectrochemical discharge under current controlled mode or voltagecontrolled mode. All operations may be monitored through a computer 100electrically connected to the position controller 30 and the powercontroller 40.

The tool 10 may be made of pure metal materials, such as tungsten orcopper, for example, to facilitate the electrolysis and theelectrochemical discharge in the electrolyte 60. Examples of theworkpiece 50, which can be machined through electrochemical discharge ofthe tool 10, include very hard non-metallic materials, such as ceramics,glass, diamond, ruby, sapphire, etc. Ceramics are commonly used for avariety of applications and are readily available.

As for the electrolyte 60, it may be made of aqueous alkaline solutionsincluding potassium hydroxide, sodium hydroxide, calcium hydroxide, andmagnesium hydroxide, for example. Such an aqueous alkaline solutionallows the current between the tool 10 and the electrode 80 to flowsmoothly, thereby easily conducting the electrolysis and theelectrochemical discharge.

The above described machining device 200 performs the electrochemicaldischarge machining as follows. A length of the tool 10 to be machinedis fixed at the lower portion of the three-dimensional feed means 20,and a height of the workpiece is upwardly positioned apart from thebottom of the electrolytic bath by the jig 71. Subsequently, theelectrolytic bath 70 is filled with the electrolyte 60 to a heighthigher than the length of the tool 10 to be machined.

As such, the electrolytic bath 70 is filled with the electrolyte 60 fromthe electrolyte-supplying tank 90, which is positioned to one side ofthe bath at the predetermined height from the bottom of the bath. Again,the electrolyte 60 can be supplied to the electrolytic bath 70 byopening the supply valve 91 of the electrolyte-supplying tank 90 (S100).

The tool 10 is immersed in the electrolyte 60 up to the length to bemachined by controlling the three-dimensional tool feed means 20 via theposition controller 30 to thereby electrochemically machine the tool 10.The electrode 80, which is laterally separated from the tool 10 at apredetermined distance, is immersed in the electrolyte 60 such that oneside of the electrode 80 is electrically connected to the powercontroller 40 and its other side is immersed in the electrolyte.

The current controlled mode of the power controller 40 is maintaineduntil the tool 10 has a desired diameter. The tool 10 serves as an anodeand the electrode 80 serves as a cathode, and direct current is appliedthereto. In such a condition, the tool 10, acting as an anode, undergoesan oxidation reaction in the electrolyte 60. As such, atoms of the tool10 are ionized into the electrolyte 60. A more vigorous oxidationreaction occurs at a position near the end of the tool 10, whichtransforms the tool into a tipped rod.

If the applied current, i.e., current density, of the surface area ofthe tool 10 exposed to the electrolyte 60 (i.e., based upon themachining state of the tool 10) is held constant, the machined portionof the tool 10 has a uniform diameter. At the electrode 80 (i.e., thecathode), a reduction reaction which generates hydrogen gas occurs. Assuch, the tool 10 may be made of tungsten, and the electrode 80 may bemade of platinum. Also, aqueous potassium hydroxide solution may be usedas the electrolyte 60.

When the tool 10 is machined to a diameter of about 0.5 mm, the molarnumber of the electrolyte 60 is about 5 mol, and the applied currentdensity ranges from about 10 to 12 mA/mm². The vertical position of thetool 10 is controlled in real-time using the three-dimensional tool feedmeans 20 so that the tool can be machined (S200). Thereafter, the heightand the concentration of the electrolyte 60 are regulated based on thematerial of the workpiece 50 positioned in the electrolytic bath 70(S300).

When the power controller 40 is switched from the current controlledmode to the voltage controlled mode, the polarities of the tool 10 andthe electrode 80 are converted to a cathode and an anode, respectively,i.e., the polarities are reversed compared with those used for theelectrolytic machining of the tool 10. Subsequently, a voltage isapplied thereto. Further, the power controller 40 is controlled to applya relatively higher voltage to the tool 10 and the electrode 80, ascompared to the electrolytic machining of the tool 10.

When this happens, the tool 10 generates hydrogen gas due to thecontinuous voltage application of the power controller 40, and theelectrode 80 is ionized through an oxidation reaction. However, theelectrode may include materials which are not easily dissolved in theelectrolyte 60, such as platinum, silver, gold, etc., so that its lossof mass is small.

Furthermore, when the voltage applied to the tool 10 exceeds apredetermined limit, sparks arise from the lower end of the tool 10having the smallest radius of curvature, and the predetermined limit ofthe voltage is changed on the basis of concentration of the electrolyte60, shape of the tool 10, and the area of the tool 10 in contact withthe electrolyte 60. Furthermore, sparks occur even at the upper portionof the tool 10 as the voltage applied to the tool 10 is increased, andit begins as a common undercurrent and develops into corona discharge,spark discharge, and arc discharge.

By controlling the power controller 40 to maintain a constant voltage,sparks can be created only at the lower end of the tool 10. At thattime, the tool 10 is perpendicularly and downwardly fed by thethree-dimensional feed means 20 to come into contact with the surface ofthe workpiece 50, thereby electrochemically machining the workpiece 50.In addition, the workpiece 50 can be machined to a desired form bycarrying out a horizontal feed as well as a perpendicular and downwardfeed of the tool 10 at the same time (S400).

Turning now to FIGS. 2 and 3, an electrolytic machining processaccording to the present invention and an electrochemical dischargemachining process according to the present invention are shown,respectively. As will be seen in FIGS. 2 and 3, the present machiningmethod allows the electrolytic machining process and the electrochemicaldischarge machining process to be carried out in the same machiningdevice 200.

First, as illustrated in FIG. 2, the tool 10 serving as an anode and theelectrode 80 serving as a cathode are immersed in the electrolyte 60.Then, when the predetermined direct current is applied thereto, acertain portion of the tool 10 is dissolved into the electrolyte 60through the oxidation reaction, and the electrode 80 generates hydrogengas through the reduction reaction. As such, if the applied current(i.e., current density) for the surface area of the tool 10 exposed tothe electrolyte 60 (based upon the machining state of the tool 10) isheld constant, the machined portion of the tool 10 has a uniformdiameter. From a standpoint of a simple electrolytic machining, the tool10 is a machining target in the machining of the tool 10.

Second, as illustrated in FIG. 3, the polarity of the tool 10 isconverted from an anode to a cathode, and the electrode 80, whichpreviously served as a cathode, is converted to an anode. Thereafter, ifthe predetermined voltage is applied thereto, a reduction reaction whichgenerates hydrogen gas occurs at the tool 10 and an oxidation reactionoccurs at the electrode 80.

When the applied voltage is increased, sparks travel from the lower endof the tool 10 to the upper portion. As such, spark emission is limitedto occur only at the lower end of the tool 10 by controlling thevoltage. Then, the tool 10 can be fed to the workpiece 50 to perform theelectrochemical discharge machining.

In the electrochemical discharge machining device and the machiningmethod, the tool 10 may be made of other pure metal materials other thantungsten or copper. Additionally, the electrode 80 may be made of othermetal materials insoluble in aqueous alkaline solution other thanplatinum, gold or silver.

As described above, with the electrochemical discharge machining deviceand the machining method according to the present invention, anelectrolytic machining process and an electrochemical dischargemachining process can be carried out in the same machining device. Thus,the machining time required to perform the process can be decreased, anderror ranges attributed to machining can be lessened. Therefore,machining and productivity of the workpiece can be improved byaccurately machining the workpiece.

More particularly, by a relatively simple operation of the mode whichprovides power and concentration of the electrolytic solution, theelectrolytic machining and the electrochemical discharge machining canbe performed together, irrespective of hardness of the workpiece. Inparticular, materials having high brittleness, such as ceramics, glass,quartz, ruby, sapphire, and diamond, can be machined.

The present invention has been described in an illustrative manner, andit is to be understood that the terminology used is intended to be inthe nature of description rather than of limitation. Many modificationsand variations of the present invention are possible in light of theabove teachings. Therefore, it is to be understood that within the scopeof the appended claims, the invention may be practiced otherwise than asspecifically described.

That which is claimed is:
 1. An electrochemical discharge machiningdevice comprising: a tool feeder and a position controller therefor; atool carried by said tool feeder; an electrode; a power controller forapplying a current to said tool and said electrode and selectivelyswitching a polarity of the current; and an electrolytic bath comprisingan electrolyte in which a workpiece is to be processed, the electrolytefor promoting an electrochemical reaction between the tool and theelectrode when immersed therein.
 2. The device according to claim 1wherein said electrolyte comprises an aqueous alkaline solution selectedfrom the group consisting of potassium hydroxide, magnesium hydroxide,sodium hydroxide, and calcium hydroxide.
 3. The device according toclaim 1 wherein said tool comprises at least one of tungsten and copper.4. The device according to claim 1 wherein said power controller appliesa direct current to said tool and said electrode.
 5. The deviceaccording to claim 1 wherein the workpiece comprises at least one ofglass, ceramic, quartz, diamond, ruby, and sapphire.
 6. The deviceaccording to claim 1 wherein said electrolytic bath further comprises anexhaust valve for removing the electrolyte from said electrolytic bath.7. An electrochemical discharge machining device comprising: anelectrolytic bath comprising an electrolyte in which a workpiece is tobe processed; a tool and an electrode to be inserted in saidelectrolytic bath; and a power controller for selectively switchingpolarities of said tool and said electrode and applying power thereto toalternately perform electrolytic machining of said tool andelectrochemical discharge machining of the workpiece.
 8. The deviceaccording to claim 7 wherein said power controller switches the polarityof said tool to a positive polarity and switches the polarity of saidelectrode to a negative polarity to perform electrolytic machining. 9.The device according to claim 7 wherein said power controller switchesthe polarity of said tool to a negative polarity and switches thepolarity of said electrode to a positive polarity to performelectrochemical discharge machining.
 10. The device according to claim 7wherein said power controller operates in a current controlled modeduring electrolytic machining and in a voltage controlled duringelectrochemical discharge machining.
 11. The device according to claim 7further comprising a tool feeder for said tool and a position controllerfor said tool feeder.
 12. The device according to claim 11 wherein saidtool feeder comprises a three-dimensional tool feeder, and wherein saidposition controller electrically controls three axial directionmovements of the three-dimensional tool feeder.
 13. A method forperforming electrochemical discharge machining of a workpiece comprisinga material, the method comprising: providing an electrolytic bathcomprising an electrolyte and placing the workpiece therein; inserting atool and an electrode in the electrolytic bath; and selectivelyswitching polarities of the tool and the electrode and applying powerthereto to alternately perform electrolytic machining of the tool andelectrochemical discharge machining of the workpiece.
 14. The methodaccording to claim 13 wherein selectively switching comprises switchingthe polarity of the tool to a positive polarity and switching thepolarity of the electrode to a negative polarity to perform electrolyticmachining.
 15. The method according to claim 13 wherein selectivelyswitching comprises switching the polarity of the tool to a negativepolarity and switching the polarity of the electrode to a positivepolarity to perform electrochemical discharge machining.
 16. The methodaccording to claim 13 wherein applying power comprises applying currentduring electrolytic machining and applying voltage duringelectrochemical discharge machining.
 17. The method according to claim13 wherein the electrolyte comprises an aqueous alkaline solutionselected from the group consisting of potassium hydroxide, magnesiumhydroxide, sodium hydroxide, and calcium hydroxide.
 18. The methodaccording to claim 13 wherein the tool comprises at least one oftungsten and copper.
 19. The method according to claim 13 wherein theelectrode comprises at latinum, silver and gold.